I can't get madsonic working together with Apache functioning as reverse proxy.

I put apache as a reverse proxy in front of all my webinterfaces. I also add basic authentication to it so that people first need to authenticate to apache before they can connect to the webinterface. This is a huge security advantage since attackers can't mess with any of my webinterfaces unless they've first authenticated to apache. This how ever is not possible if the web interface it self is already using http basic authentication, since you can't chain two of those together. Unfortunately madsonic is using basic authentication, so I can't do that. (couchpotato, sickrage, roundcube, owncloud, postfixadmin, etc... all use a different form of authentication with cookies). Nevertheless, I do want apache in front of madsonic as a reverse proxy because I think the ssl stack of apache is a lot more bullet proof since I can configure which ciphers to use etc..

since madsonic has its own usermanagement, you do not need a pre authentication. and due to routing from an external interface to an internal. they can't mess around, cause the rout / proxy will brake up.

but i know your problem ... madsonics call to elements are path absolute and not relative. so without mapping this proxy to "root" -> / the styling and other stuff will end up in 404

So yea... I'm giving up on this for now and I'll simply run it on a different port without the /madsonic suffix. But it should be possible to get it working with that suffix.

since madsonic has its own usermanagement, you do not need a pre authentication.

I disagree with that. Madsonic is a small project and there is a large chance there are security bugs in it. Apache which is deployed by a significantly larger user base is most likely a much harder target to break into than madsonic. So I prefer first authenticating with Apache before you're allowed to Authenticate with Madsonic. It's security in depth.